Method and apparatus for forming materials



A. W. KORB Sept. 18, 1956 METHOD AND APPARATUS FOR FORMING MATERIALSFiled July 31, 1951 3 SheetsSheet 1 INVENTOR.

BY- dav Sept. 18, 1956 A. w. KORB 2,763,040

METHOD AND APPARATUS FOR FORMING MATERIALS Filed July 31 1951 3Sheets-Sheet 2 IN V EN TOR.

Sept. 18, 1956 w KORB 2,763,040

METHOD AND APPARATUS FOR FORMING MATERIALS Filed July 31, 1951 3Sheets-Sheet 3 IN V EN TOR.

E 2,763,040 METHGD AND APPARATUS FOR FORMING MATERlALS Anton W. Kerb,Grandville, Mich., assignor to Jervis Corporation, Graudville, Mich, acorporation of Michigan Application July 31, 1951, Serial No. 239,587Claims. (Cl. 2257.2)

This invention relates to a method and apparatus for forming materialsand to the products obtained therefrom. It is an object of the inventionto provide materials and an improved method and apparatus of thatcharacter.

It is another object of the invention to provide an improved method andapparatus for producing castings in a continuous operation.

it is another object of the invention to provide an improved method andapparatus for producing stronger magnets from a given material than hasheretofore been possible.

it is another object of the invention to provide an improved permanentmagnet which is stronger than previously known magnets formed of thesame materials.

In accordance with one feature of the invention, a method and apparatusare provided whereby the casting of material may be carried oncontinuously and whereby the material is subjected to high frequencyvibration as it cools. Castings are thereby produced very economically(several steps of the conventional methods being eliminated) and, at thesame time, the castings are greatly improved in quality, particularly,it is believed, in grain size and molecular structure, all as will beexplained subsequently in detail.

The invention is Well adapted to the making of magnets, of both thepermanent type and the electromagnetic type. That is, the invention isof particular value in producing both permanent magnets and the cores ofelectromagnets. in accordance with another feature of the invention, aD. C. field is applied to the material (which in this instance must bepermanently magnetizable) in conjunction with the high frequencyvibration referred to above, as the material cools, whereby permanentmagnets of great magnetic strength are produced. Preferably, but notnecessarily, this method and apparatus provide for continuous casting,as suggested above.

It is a well recognized principle in the art of producing permanentmagnets that if the magnetic material from which a magnet is to beproduced is heated above its Curie point and then allowed to cool whilea magnetizing force is applied thereto, the resultant magnet will bestronger than if the material were subjected to a magnetizing force onlywhile cool or below its Curie point. According to a generally acceptedtheory the reason for this is that the heating of the material to atemperature above its Curie point, and preferably to a molten orsemimolten state, relaxes the crystalline structure of the material suchthat the individual magnetic particles, commonly called spins ormagnetic domains, are no longer tightly bound together with theirmagnetic axes in any fixed relative orientation and may be brought morecompletely into alignment by application of a magnetizing force thanwould otherwise be possible. After the material has been allowed to coolbelow its Curie point with the magnetizing force continuously applied,the magnetic domains again become locked into position but with theiraxes to a substantial degree aligned.

This applies, of course, only Where the material used is susceptible ofpermanent magnetization. If a material such as soft iron, for example,is subjected to such a magnetizing operation, a permanent magnet is notproduced since the crystalline structure of such material atent will notlock the individual magnetic domains, or any large percentage of thesame, into any particular orientation with respect to each other.However, Where the material employed is one which is capable of beingpermanently magnetized, the crystalline structure is such as to lock theaxes of the individual magnetic domains, or at least an effectivepercentage thereof, into definite aligned orientation.

It is believed that the degree to which the magnetic domains areliberated one from the other by elevation of the temperature of amaterial above its Curie point is limited. The extent to which theindividual magnetic domains are so liberated is probably dependent uponthe degree to which original groups of associated magnetic domains arebroken down by the application of heat into smaller groups of varyingsize, the individual magnetic domains presumably being more nearly freeto align themselves with an applied magnetic field where they areincluded in small residual groups. In any event, it is believed that theextent to which the axes of the in dividual magnetic domains may bealigned even when the material is heated above its Curie point is one ofdegree.

According to the last-mentioned feature of the invention this effect ofraising the temperature of a magnetic material above its Curie point isaugmented by rapid vibration of the magnetic domains thereof, a secondfactor thereby being introduced which tends to liberate the individualmagnetic domains within the material from each other such that they maybe aligned to a greater degree by an applied magnetizing force. It isanother object of the invention to provide an improved method andapparatus for producing stronger permanent magnets by more completelyaligning the axes of the individual magnetic domains than has heretoforebeen possible.

Where permanent magnets have been produced in the past by heatingpermanently magnetizable material above its Curie temperature and thensubjecting the material to a magnetizing force while the material isbeing cooled, a batch process has been employed, usually involving theuse of molds and necessarily involving a substantial amount of labor.According to another feature of the invention magnets are produced in acontinuous process with flowable (i. e. molten or semimolten),permanently magnetizable material being withdrawn from a container andsubjected to a magnetizing force while being cooled, the entire processbeing continuous as long as the supply of molten material is available.

It is another object of the invention to provide an improved method andapparatus for producing permanent magnets continuously as opposed toproducing them in batches.

In accordance with one embodiment of the invention which incorporatesall of the features of the invention referred to above, the material ofwhich castings are to be made is heated to a molten state in a vesseland is allowed to escape through an opening in the bottom thereof andpass through a continuously cooled die which forms the rapidly hardeningmaterial to the desired cross section. As the material first enters thedie it is in a molten state but as it passes through the die it coolswith sufiicient rapidity that when it leaves the die it is at leastself-supporting and, where permanent magnets are being made, well belowthe Curie temperature for the particular material.

Means are provided for causing rapid vibration of the material as itleaves the vessel and enters the die, the vibrations preferably being ofsupersonic frequency. Such vibration of the material results in castingsof finer grain and greater homogeneity than can otherwise be obtained.Where permanent magnets are being made, means are provided for producinga powerful magnetic field within the die for magnetizing the material asit cools. Finally, means are preferably provided for continuouslydrawing the completed product out of the die As will subsequently beexplained in greater detail magnets produced by this method, more spec1iically 1n which the material forming the magnets is sub ected tosupersonic vibrations during the simultaneous cooling and magnetizingoperations, are substantially stronger magnetically than magnetsproduced by the conventional or previously known methods. Also magnetsmay be produced continuously by such a method and apparatus whereby asubstantial saving is eifected in labor cost as compared to methods andapparatus based upon a batch process.

Accordingly, it is another object of the mventron to provide an improvedmethod and apparatus for producing in a continuous operation permanentmagnets of great magnetic strength.

This invention, together with further O-bjCClS and ad vantages thereof,will best be understood by reference to the following description takenin connection Will? the accompanying drawings, and its scope will bepointed out in the appended claims.

In the drawings, in which like parts are deslgnated by like referencenumerals,

Fig. 1 is a cross-sectional view, partially schematic, of apparatus,constructed in accordance with one embodiment of the invention, forcontinuous product-ion of castings, and, more specifically, permanentmagnets;

Fig. 2 is a partial cross-sectional view of apparatus similar to thatdisclosed in Fig. l but illustrating another embodiment of theinvention;

Fig. 3 is a view similar to Fig. 1 but illustrating still anotherembodiment of the invention;

Figs. 4, 5 and 6 are graphs showing one form of the magnetizing andvibrating current and its components which may be employed in theapparatus shown in Fi 3;

i igs. 7, 8 and 9 are graphs showing another form of magnetizing andvibrating current which may be employed in the apparatus shown in Fig.3; and

Fig. 10 is a partial cross-sectional view of apparatus similar to thatdisclosed in Fig. 3 but illustrating still another embodiment of theinvention.

The embodiments of the invention disclosed in Figs. 1, 2, 3 and 10 arecomplete with means which are needed only in the production of permanentmagnets, and the following description of the various illustratedembodiments includes the steps of one method and the portions of theapparatus used only in the making of permanent magnets. However, theinvention is not limited in application to the production of magnets buthas application to the production of castings in general, in which casecertain steps of the disclosed method and certain portions of thedisclosed apparatus are unnecessary.

The apparatus disclosed in Fig. 1 includes a crucible 11 containing aquantity of material 12 from which castings, and, in particular,permanent magnets, are to be formed. The material 12 may be of anysuitable metal which is capable of being permanently magnetized and, inaccordance with the illustrated embodiment of the invention, is broughtto a molten or semimolten state through induction heating by a currentpassing through a coil 13 which surrounds the crucible. The leads 14 and15 of the coil 13 are of course connected to any suitable source ofrelatively high frequency electric current, such source not beingillustrated in the drawings.

A valve in the form of a rod 16 of a suitable refractory materialextends down through the molten metal 12 to control the flow of metalthrough an opening 17 in the bottom of the crucible. Located immediatelybelow the opening 17 is a die 18 having an opening 19 therethrough whichis of the same cross section as that desired in the magnet or magnets tobe produced.

The die 18 is preferably hollow in order that it may be cooled by wateror any other suitable cooling medium. The cooling medium may be pumpedthrough a pipe 20 into a cooling chamber 21 within the body of the die18 and drawn off through a pipe 22.

When the metal in the crucible 11 has been heated to the propertemperature by the coil 13 the rod 16 may be raised permitting themolten metal 12 to escape through the opening 17 and pass through thedie opening 19. The metal 12 is cooled rapidly as it passes through thedie and is in a solid state as it leaves the die. The solidified metalbar or rod 12a then passes between a pair of rollers 23 which are drivenby any suitable power means, not illustrated in the drawings, such thatthey draw the solidified metal bar or rod downwardly. In starting suchan operation, it is desirable that a short length of rod or bar, notshown in the drawings, be used as a lead to retard the initial flow ofthe melted metal 12 through the die opening 19. Such a bar or rod may beinserted upwardly between the rollers 23 and into the die opening 19 andis preferably only slightly smaller in cross section than the dieopening. When the rod 16 is raised allowing the molten metal 12 to flowdown to the upper end of the lead bar the rollers 23 can be started andwill withdraw the lead bar and, subsequently, the metal bar 12a at sucha rate as to permit the molten metal 12 to solidify before it passescompletely through the die.

A portion of the outer wall of the cooling chamber 21 comprises atransducer 24 for transmitting physical vibrations through the water inthe cooling chamber and through the inner wall of the die 18 to thematerial 12 within the die opening 19. The transducer 24 is energizedelectrically through a pair of leads 25' and 26 and a high frequencyelectrical generator 27, the lead 26 passing through a suitableinsulating grommet 28 in one wall of the die structure. The transducer24 may be of various materials, for example, a titanate ceramic. Theprincipal characteristic of the transducer required in this applicationis that is be capable of producing mechanical vibrations of highfrequencies upon suitable electrical energization thereof. Manymaterials capable of producing this result are well-known in the art andaccordingly, the transducer will not be further described herein.

The high frequency vibrations, which are preferably supersonic infrequency, transmitted to the molten and semimolten material 12 Withinthe die opening 19 by the transducer 24, break up the crystallinestructure of the material during the solidifying of the material. Theresult is the production of castings having a very fine grain and hencehaving much greater strength. Furthermore, this is accomplished in asingle step, that is, without the necessity of additional handling orreheating of the material.

Where the end product is to be permanent magnets, the high frequencyvibration of the material produces not only a finer grain butmagnetically stronger magnets. This may be explained on the theory thatthe vibration tends to break up the residual groups of magnetic domainsinto smaller units, whereby a larger percentage of the magnetic domainscontained Within any given portion of 1tihelzdmaterial 12 may be alignedwith an applied magnetic Means for producing such a magnetic field areillus trated in Fig.1 and include a yoke 31, a coil 32 having leads 33and 34, and a D. C. generator 35. The output of the D. C. generator 35passes through the coil 32 and sets up a strong magnetic field withinthe yoke 31. It will be noted that the yoke is substantially U-shaped,the upper arm terminating alongside the upper wall of the die structure18, and the lower arm extending toa position below the die 18 and havingan opening 31a through which the completed product may pass. Prefer-'ably, the upper wall of the die structure is of magnetic matenal and theinner wall of nonmagnetic material, whereby the magnetic flux lines tendto pass from the end of the upper arm of the yoke to the material withinthe die opening 19. The flux lines then pass downwardly through themolten, semimolten, and finally the solidified portions of the materialand to the lower arm of the yoke 31 across the air gap within theopening 31a.

In accordance with this embodiment of the invention, as applied to theproduction of permanent magnets, the material of which the magnets areto be formed is subjected to high frequency vibrations originating fromthe transducer 24 during the time that the material is solidifying andcooling to a temperature below its Curie temperature, the material beingsubjected to a powerful, continuous magnetic field throughout the entireprocess. The permanent magnets produced by this apparatus and by themethod described are stronger magnetically, for any given permanentlymagnetizable material, than can be obtained by presently known apparatusand methods.

Where castings are desired of any nature other than permanent magnetsthe magnetizing means 3135 are, of course, unnecessary. The transducer24- along with the means for emergizing the transducer are desirable,however, since the high frequency vibration of the casting materialduring its solidification produces fine grain structure with a minimumof apparatus and with no additional handling of the material.

The apparatus disclosed in Fig. 2 is very similar to that disclosed inFig. 1 and described above but differs in the form of the transducer. InFig. 2 an electromagnetic transducer 36 is employed which comprises acoil 37 and a movable core or armature 38. The coil 37 is energized by ahigh frequency generator 39 which causes the armature 38 to vibrate atthe same high frequency. The vibrations of the armature are transmittedthrough the water in the cooling chamber 21 and through the inner diewalls to the molten and semimolten material, the same as in theapparatus disclosed in Fig. 1. Two forms of transducer are thereforeshown in Figs. 1 and 2, respectively. However, the invention isobviously not limited thereto but includes within its scope any form ofapparatus or device capable of causing high frequency mechanicalvibrations to be transmitted to the material contained within the dieOpening 19.

The apparatus disclosed in Fig. 3 is generally similar to that disclosedin Figs. 1 and 2 and described above but differs substantially in theform of apparatus employed for breaking up the crystalline structure ofthe In this embodiment of the of the die 18 and closely adjacent the dieopening 19, an electric coil 46 which is connected to electricalapparatus designated by the numeral 41 and shown in block form inFig. 1. The electrical apparatus 41 may comprise merely a source of D.C. voltage, the direct current obtainedtherefrom, upon passing throughthe coil 4%, establishing a magnetic field within the die opening 19 andthereby magnetizing the metal passing therethrough by aligning themagnetic domains thereof. It will be recognized that the metal formingthe die 18, or, at least that portion of the die forming the opening 19,should be nonmagnetic, since the magnetic field within the die opening19 would otherwise be very weak or even negligible.

As previously indicated, when magnetizable metal is in a molten state orabove its Curie temperature the magnetic domains of the metal arerelatively free to change the orientation of their axes and thereforemay be more completely aligned by a magnetic field than when the samematerial is at a temperature below its Curie point. Accordingly, amagnetic field of given strength will produce a stronger magnet when thefield is applied to the magnet metal in a molten state and the metalpermitted to cool within the field, than when the field is applied tometal at a temperature below its Curie point.

The method and apparatus so far described in connection with Fig. 3 areparticularly desirable as they take advantage of this principle whilestill being adapted to a continuous rather than a batch operation.

conventionally, molten or semimolten material is poured or forced into amold or die until the latter is filled, after which the material in themold or die is subjected to a magnetizing force until it is cooled belowits Curie temperature. Such a process may be classified as a batchprocess and is relatively expensive since the individual magnets soformed must be handled a number of times after the pouring operation. Inthe case of the method and apparatus so far described a continuousmagnetic bar is formed which may subsequently be divided into a largenumber of individual magnets, the entire bar being formed in acontinuous operation. A bar of any desired length may be produced bythis method if means are made available for providing a continuous flowof molten metal. For example, molten metal may be added to the crucible11 or solid metal added and the coil 13 made of such capacity as to meltthe metal as fast as it is withdrawn through the opening 17. Whether ornot the supply of metal in the crucible is replenished the process sofar described is considered a continuous process as opposed to a batchprocess. Where the term continuous process is employed herein it isintended that it be so construed.

The method and apparatus so far described, then, in connection with Fig.3 effect a substantial saving in the labor cost previously involved inthe production of magnets. The substantial reduction in the cost ofmagnets thereby obtained is a vital matter where a large number ofmagnets are employed in a device, such as a refrigerator, in a highlycompetitive field.

In accordance with another feature of the invention the electricalapparatus 41 causes a current to tlow through the coil 40 which is not adirect current of constant value but is instead of a character whoseeffect, at least, is similar to that of the current indicated in thegraph comprising Fig. 6, in which current, I, is plotted against time,t. The wave form of the illustrated current is essentially that of asquare wave pulsating direct current, such as is illustrated in Fig. 5,having superimposed thereon an inphase alternating current, such as isillustrated in Fig. 4.

A wave shape such as that shown in Fig. 6 may be produced by any one ofvarious well-known or obvious expedients and since the particular methodor apparatus used to produce the desired current is not, in itself, apart of the invention, the apparatus is not shown or described in detailherein. The desired characteristics of the current wave are that thecurrent value alternates rapidly between a substantial value of onepolarity and a relatively small value of the opposite polarity, thefrequency of the alternation being rapid and preferably in the range ofsupersonic frequencies.

One form of apparatus for producing such a wave form is a square wavegenerator and a source of high frequency alternating current such as anoscillator, the output of the latter being of the same frequency and inphase with the output of the square wave generator. This phaserelationship may be accomplished by driving the D. C. generator and anA. C. generator at the same effective speed or by providing a suitablecontrol circuit whereby the alternating current voltage triggers thesource of square wave direct current. Another obvious expedient involvesthe combination of an alternating current of substantial peak value, seeFig. 7, and a steady state direct current whose value is somewhat lessthan the peak value of the A. C., see Fig. 8. The resultant Wave formwould be that illustrated in Fig. 9 where it is seen that the wave hasthe same desired characteristics as the wave illustrated in Fig. 6,namely the current alternates rapidly between a substantial value of onepolarity and a relatively small value of the opposite polarity.

The beneficial efiiect of such a wave form will be eX- plained inaccordance with the theory previously presented. When the metal 12enters the die opening 19 and While it is still molten or semimolten, orin any event while it is still above the Curie temperature of thematerial, the magnetic domains of the metal are contained probablywithin relatively small and loosely associated groups of domains.Accordingly, the axes of the domains are responsive to the weak magneticfield established by the relatively small negative half cycle of thecurrent through the coil 4t) (referring to either Pig. 6 or Fig. 9) asWell as to the much stronger magnetic field produced by the positivehalf cycle of the current flowing in the coil. As a result theindividual magnetic domains are rapidly oscillated presumably through anangle of substantially I80 degrees, and thereby tend to shake themselvesloose from any remaining influences within the metal which may tend tolock them in a given orientation either with respect to the body of themetal or with respect to other associated magnetic domains. In otherWords, the application of the rapidly alternating magnetic field to thesoft metal for even a very short period of time tends to break up anyremaining groups of magnetic domains or to break down any otherrestraining infiuences which may be present in the metal, and thereby torender the individual magnetic domains relatively free to alignthemselves more perfectly with any applied magnetic field or force.

As the metal passes through its Curie temperature the magnetic domainsbegin to lock into a given orientation with respect to the body of themetal. Under these conditions the relatively weak field produced by thesmall negative half cycle of the current wave fails to cause asubstantial movement or reorientation of the individual magneticdomains, while the relatively strong field produced by the positive halfcycle of the current wave still forces the individual magnetic domainsto align themselves with that field.

It will be apparent, then, that a single coil carrying an alternatingcurrent of which alternate half cycles are of substantially greatermagnitude than the other alternate half cycles, can serve the dualpurpose of oscillating the magnetic domains of metal above its Curietemperature and aligning the magnetic domains of the same metal as itpasses through its Curie temperature.

In accordance with the embodiment of the invention illustrated in Fig.10 an alternating voltage derived from a suitable source 42 is appliedto a coil 43, through the field of which molten or semimolten metalpasses. A second coil 44 is arranged over the coil 43 and is connectedto a suitable source 45 of direct current voltage.

The voltage of the two sources 42 and 45 are of such value that thepeaks of the A. C. current wave through the coil 43 are of slightlygreater value than the value of the D. C. current in the coil 44. Theeifect is then the same as in the previously described embodiment.Namely, the metal within the die 18 is subjected to a magnetic fieldwhich alternates rapidly between a substantial value and a relativelyweak value.

In accordance with either of the embodiments disclosed in Figs. 3 and10, the metal which is to form the ultimate magnet or magnets issubjected while above its Curie temperature to a rapidly alternatingmagnetic field which tends to liberate the individual magnetic domainsto a greater degree than is accomplished by merely heating metal aboveits Curie temperature. The magnets so produced from any givenpermanently magnetizable material are stronger magnetically than magnetsproduced of the same material by any previously known method orapparatus.

It will be apparent from the foregoing that the invention includes anumber of associated features. By way of example, it is pointed out thatthe invention includes a novel method and apparatus for continuousproduction of castings having a fine grain structure. It also includes anovel method and apparatus for producing stronger permanent magnets,which method and apparatus may or may not provide for continuous castingof the magnets. Still further, the invention covers improved permanentmagnets and improved castings in general.

it will be apparent that the invention may be varied in its physicalembodiment without departing from the spirit of the invention, and it isdesired, therefore, that the invention be limited only by the prior artand the scope of the appended claims.

The invention having thus been described, What is claimed and desired tobe secured by Letters Patent is:

1. The method of producing permanent magnets which comprises, subjectingpermanently magnetizable material to a magnetizing force and vibratingsuch material at ultrasonic frequency while cooling the material from atemperature at which the material is substantially nonmagnetic to atemperature at which the material is magnetic.

2. The method of producing permanent magnets which comprisescontinuously driving permanently magnetizable material through amagnetizing field while simultaneously vibrating such material atultrasonic frequency and cooling the material from a temperature atwhich the material is substantially nonmagnetic to a temperature atwhich the material is magnetic.

3. Apparatus for producing permanent magnets which comprises means forcreating a magnetic field which comprises a steady state field and alarger field alternating at ultrasonic frequency whereby the net fieldalternates at ultrasonic frequency between a substantial value in onedirection and a relativelysmall value in the opposite direction, meansfor heating permanently magnetizable material to a temperature at whichsuch material is substantially nonmagnetic, means for advancing suchmaterial through said field, and means for cooling the material while insaid field to a temperature at which the material is magnetic.

4. Apparatus for producing permanent magnets which comprises anelectrical coil, electrical means for producing in said coil an electriccurrent comprising a direct current and a larger current alternating atultrasonic frequency whereby the net current alternates at ultrasonicfrequency between a substantial value in one direction and a relativelysmall value in the opposite direction, means for heating permanentlymagnetizable material to a temperature at which such material issubstantially nonmagnetic, means for advancing such material throughsaid field, and means for cooling the material while in said field to atemperature at which the material is magnetic.

5. Apparatus for producing permanent magnets which comprises means forheating permanently magnetizable material at least to a temperature atwhich said material is semimolten, a die for continuously forming saidmaterial to a desired cross section as said material passestherethrough, means for creating a magnetic field within said die, meansfor vibrating said material within said die at ultrasonic frequency, andmeans for cooling said material while in said field to a temperature atwhich the material is magnetic.

References Cited in the file of this patent UNITED STATES PATENTS1,477,847 Palmer Dec. 18, 1923 1,978,222 Otte Oct. 23, 1934 2,284,703Welblund et al. June 2, 1942 2,284,704 Welblund et al. June 2, 19422,419,373 Schrumn Apr. 22, 1947 2,503,819 Gunn et al. Apr. 11, 19502,569,468 Gaugler Oct. 2, 1951 FOREIGN PATENTS 572,409 Great BritainOct. 8, 1945

